Tuning Electronic Structures of Carbazole‐Cyanostyrene Molecules to Achieve Dual‐State Emission for Trace Water Analysis, Picric Acid Sensing, and Reversible Mechanofluorochromism

Abstract

Dual-state emissive (DSE) materials with efficient emission both in solution and in the solid state can be used in complex environments. In this work, we demonstrate the synthesis of DSE materials by finely tuning the electronic structures of luminogens. Four carbazole-cyanostyrene compounds with different terminal groups, i. e., CZ-Ph-H without additional substituent, CZ-Ph-TA with an N,N-dimethylamino functional group, CZ-Ph-CN with a cyano group, and CZ-Ph-TB with a tbutyl group, have been synthesized and their photophysical properties are fully investigated by spectroscopic studies, theoretical calculations, and crystallographic analysis. Interestingly, while CZ-Ph-H, CZ-Ph-CN, and CZ-Ph-TB are aggregation-induced emissive (AIE) molecules only showing strong emission in the aggregated states (aggregate suspension and solid powder), CZ-Ph-TA is a DSE molecule showing strong emission in both dilute solution and aggregated states. In addition, CZ-Ph-TA could serve as a fluorescent probe for trace water analysis in organic solvents and picric acid (PA) detection in both dilute solution and aggregate suspension. CZ-Ph-TA also exhibits reversible mechanofluorochromism with a spectral shift of 21 nm. The synthesis of the N,N-dimethylamino-substituted molecule with excellent photophysical properties represents an important attempt to achieve DSE by finely tuning the electronic structures of molecules.

One-Step Transformations from ACQ Luminogens to DSEgens via the Boc Protection Process

“…However, in the excited states, electron densities have been largely shifted from the electron-rich indole group to the electron-poor group as seen in their LUMO. Such a distribution also indicates that electrons within molecules can migrate from electron donors to electron acceptors upon excitation, indicating an explicit ICT process. , In addition, the ICT nature of the two molecules may explain their fluorescence sensitivity to solvent polarity.…”

“…Such a distribution also indicates that electrons within molecules can migrate from electron donors to electron acceptors upon excitation, indicating an explicit ICT process. 30 , 40 In addition, the ICT nature of the two molecules may explain their fluorescence sensitivity to solvent polarity.…”

Symphony of light: AIE and MFC in carbazole-based cyanostilbenes

“…28). 93 The influence of the electronic factors of the substituent groups on the photophysical properties was analysed. It is interesting to note that just one of the four molecules, 42b , demonstrates dual-state emission (DSE) behaviour, whilst the other three molecules show normal AIE behaviour.…”

Dual emission and its λ-ratiometric detection in analytical fluorimetry. Pt. I. Basic mechanisms of generating the reporter signal

“…The dyes demonstrating strong spectral shifts on transition to ICT states are commonly organic molecules with well-developed π-electronic structures that demonstrate very strong polarity-dependent shifts of fluorescence spectra. Their development continues for applications in λ-ratiometric sensing [46][47][48][49] and imaging [50][51][52].…”